The technical field of this invention concerns methods and compositions for removing moisture through chemical reaction and, in particular, the removal of moisture from environments containing epoxy adhesives.
Entrapped moisture is a major concern in many industrial and commercial products because of the damaging effects it can have on operating systems or delicate components. For example, manufacturers of electronic parts and packages often must take expensive and time-consuming steps to hermetically seal moisture out of their products. High temperatures and vacuums or dry nitrogen atmospheres are often employed to remove moisture prior to the sealing of electronic packages. Eutectic bonds are used rather than polymeric adhesives within the sealed packages to avoid the reintroduction of moisture. The acceptable moisture level for many electronic devices can be as low as 5,000 or even 2,000 parts per million (ppm). However, even when hermetic sealing steps are taken, it is often difficult to maintain these standards.
Eutectic bonding typically involves the use of a two phase, e.g., gold and silicon, conductive solder to join an electronic chip, die or other component to its packaging in a moisture-free fashion. The materials that form eutectic solders are expensive and the bond coverage they provide is often less than the full area on which the chip or die component overlies its substrate. This disparity in coverage is a source for stress development that can distort and damage the circuitry. Moreover, the high temperature necessary to induce eutectic bonding, i.e., 400.degree. C. to 500.degree. C., imposes restrictions on component selection and adds to the processing time and costs.
Until now epoxy adhesives have not been considered suitable for use within sealed electronic packages where moisture constraints are present. A reason is that the epoxy compositions themselves often contain moisture which is expelled into the sealed package during the life of the component. Moisture constraints are particularly troublesome for epoxy-containing packages when the finished product is exposed to elevated temperatures, i.e., 150.degree. C. to 250.degree. C., for extended periods of time.
There accordingly exists a need for better methods and compositions for maintaining substantially moisture-free environments for industrial and commercial products, particularly electronic packages. Adhesives that are inexpensive, provide high adhesive coverage and do not release moisture would satisfy a long-felt need in industry, particularly if they could be applied at lower temperatures than eutectic solders and maintain package moisture levels below 5000 ppm.